The effect of installation

You can see the effect of installing multiply-by-seven by
evaluating the following sample. Place the cursor after the following
expression and type C-x C-e. The number 21 will appear in the
echo area.

(multiply-by-seven 3)

If you wish, you can read the documentation for the function by typing
C-h f (describe-function) and then the name of the
function, multiply-by-seven. When you do this, a
*Help* window will appear on your screen that says:

multiply-by-seven is a Lisp function.
(multiply-by-seven NUMBER)
Multiply NUMBER by seven.